In communication networks, there is always a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communication network is deployed.
In wireless communications networks there is currently a lot of available spectra in unlicensed frequency bands. These bands are currently widely used by Wi-Fi. The sharing of the spectrum in Wi-Fi is done by dividing the total bandwidth into a number of channels. In the 2.4 GHz frequency band the channels are typically around 20 MHz wide, and up to 13 channels are defined. These channels are partially overlapping, and thus will interfere with each other. Three non-overlapping channels may be used in the 2.4 GHz band. For the 5 GHz frequency band more channels are available as the available bandwidth is larger. With the development of IEEE 802.11n and IEEE 802.11ac, the bandwidth has been increased from 20 MHz to 40, 80, and even 160 MHz. Thus, in particular when wider bandwidths are used, the number of non-overlapping channels is still rather small.
In common deployments of Wi-Fi, the access points (APs) are allocated such that the used channels, as far as possible, are not overlapping. In practical deployments this may involve the distance between APs using the same channel to be maximized.
Carrier sense multiple access with collision avoidance (CSMA/CA) is used for channel access. In general terms, this means that the channel is sensed, and only if the channel is declared as Idle, a transmission is initiated. In case the channel is declared as Busy, the transmission is deferred until the channel is found Idle. When the coverage areas of several APs overlap, this means that transmission related to one AP might be deferred in case a transmission to another AP which is within range can be detected. Effectively this means that if several APs are within range, they will have to share the channel in time, and the throughput for the individual APs may be severely degraded.
The main principle behind so-called cognitive radio is that an un-licensed user may be able to use licensed spectrum in case no licensed user (i.e., a white space; in telecommunications, white spaces generally refer to frequencies allocated to a broadcasting service but not used locally) is operating at a certain area. In general terms, the unlicensed user senses a certain spectrum and if no licensed user is presently transmitting the unlicensed user is allowed to use that spectrum for communication. The sensing typically has to continue during the communication since if any licensed user starts to use the spectrum the unlicensed users typically need to terminate the communication. Hence cognitive radio application may have time-varying connections in the sense that different spectrum parts are used at different time.
The principles of sensing a spectrum and allocate a spectrum part to an unlicensed user when the spectrum is not used is known in the art. However, one issue concerns the fact that no considerations are made with respect to the fact that cellular communication networks, such as 3GPP (Third Generation Partnership) Long Term Evolution (LTE), have a variable bandwidth for determination of how much bandwidth one can allocate.
Cellular radio access technologies, such as 3GPP LTE communications may thus be used in unlicensed frequency bands, such as the industrial, scientific and medical (ISM) band. One approach is to use LTE on a best effort basis, when carrier aggregation is employed. Specifically, the unlicensed band is used for a secondary cell (SCell) to a Primary cell (PCell) that is operating in a licensed spectrum. In this way the connection to a served device may still be maintained via at least the PCell in case the SCell may be interfered by, say, Wi-Fi or Bluetooth.
Carrier Aggregation is known in the art and is defined from 3GPP Release 10. However, the prior art does neither address allocation approaches, nor possible interference scenarios (e.g., how to handle transmissions from Wi-Fi, or Bluetooth transmitters) that may occur once LTE is deployed in an unlicensed frequency band. Further, in case the ISM band is to be shared between, for instance, Wi-Fi and LTE, it may be beneficial that LTE does not impact the performance of Wi-Fi. Because Wi-Fi is based on CSMA/CA, an LTE signal may effectively force a Wi-Fi transmitter to defer its transmission as long as the LTE signal is present. Thus, the performance for Wi-Fi may be severely degraded.
Therefore, there is a need for a flexible channel allocation for allocating LTE in unlicensed frequency bands.
Hence, there is still a need for an improved channel allocation in unlicensed frequency bands.